Alternative transportation fuels have been represented as enablers to reduce toxic emissions in comparison to those generated by fossil and other conventional fuels used in reciprocating combustion-type engines. At the same time, tighter emission standards and significant innovation in catalyst formulations and engine controls has led to dramatic improvements in the low emission performance and robustness of conventionally fueled engine systems. Although these improvements have reduced the environmental differential between optimized conventional and alternative fuel vehicle systems, many technical challenges remain in order to make the conventionally-fueled internal combustion engine a nearly zero emission system having the efficiency necessary to make a host vehicle commercially viable.
Alternative fuels cover a wide spectrum of potential environmental benefits, ranging from incremental toxic and carbon dioxide (CO2) emission improvements such as those facilitated by reformulated gasoline, alcohols, liquid petroleum gas (xe2x80x9cLPGxe2x80x9d), and the like; to significant toxic and CO2 emission improvements such as those facilitated by natural gas, dimethyl ether (xe2x80x9cDMExe2x80x9d), and the like. Hydrogen is clearly the ultimate environmental fuel, with potential as a nearly emission-free engine fuel. Unfortunately, the market-based economics of alternative fuels and new power train systems are uncertain in the short to mid-term.
The automotive industry has made significant progress in reducing automotive emissions in both the mandated test procedures and in actual use. This has resulted in added cost and complexity of engine management systems. However, some of those costs are offset by other advantages of computer controls such as increased power density, fuel efficiency, drivability, reliability, and real-time diagnostics.
Future initiatives to require zero emission vehicles appear to be taking us into a new regulatory paradigm where asymptotically smaller environmental benefits come at a very large incremental cost. Yet, even an xe2x80x9cultra low emissionxe2x80x9d certified vehicle can emit high emissions in limited extreme ambient and operating conditions or with failed or degraded components.
One approach to addressing the issue of emissions is the employment of fuel cells, such as solid oxide fuel cells (xe2x80x9cSOFCsxe2x80x9d), in an automobile. A fuel cell is an energy conversion device that generates electricity and heat by electrochemically combining a gaseous fuel, such as hydrogen, carbon monoxide, or a hydrocarbon, and an oxidant, such as air or oxygen, across an ion-conducting electrolyte. The fuel cell converts chemical energy into electrical energy, which may then be used by a high-efficiency electric motor, or stored. SOFCs are currently constructed of solid-state materials, typically utilizing an ion conductive oxide ceramic as the electrolyte. A conventional electrochemical cell in a SOFC is comprised of an anode and a cathode with an electrolyte disposed therebetween. The oxidant passes over the oxygen electrode or cathode while the fuel passes over the fuel electrode or anode, generating electricity, water, and heat.
In a typical SOFC, a fuel flows to the anode where it is oxidized by oxygen ions from the electrolyte, producing electrons that are released to the external circuit, and mostly water and carbon dioxide are removed in the fuel flow stream. At the cathode, the oxidant accepts electrons from the external circuit to form oxygen ions. The oxygen ions migrate across the electrolyte to the anode. The flow of electrons through the external circuit provides for consumable or storable electricity. However, each individual electrochemical cell generates a relatively small voltage. Higher voltages may be attained by electrically connecting a plurality of electrochemical cells in series to form a stack.
Although any number of cells may be combined to form a stack having a desired output voltage, very tall stacks may incur several undesirable characteristics such as difficult maintenance and repair, awkward packaging, unequal and inefficient operating temperatures between center cells and end cells, unequal fuel distribution under varying fuel flow rates, high internal impedance, and inefficiency under rapidly varying output loads.
A SOFC cell stack also includes conduits to allow passage of the fuel and oxidant into, and byproducts as well as excess fuel and oxidant out of the stack. Generally, oxidant is fed to the structure from a manifold located on one side of the stack, while fuel is provided from a manifold located on an adjacent side of the stack. The fuel and oxidant are generally pumped through the manifolds and introduced to a flow field disposed adjacent to the appropriate electrode. The flow fields that direct the fuel and oxidant to the respective electrodes typically create oxidant and fuel flows that are perpendicular to one another across the electrodes.
Seals are provided around the edges of the various cell stack components to inhibit crossover of fuel and/or oxidant. For example, seals are disposed between the electrodes and adjacent flow fields, around manifolds, between flow fields and cell separators, and elsewhere.
Advantages are achieved and drawbacks and disadvantages of the prior art are overcome or alleviated by providing a fuel and air supply base manifold for a modular solid oxide fuel cell assembly having a plurality of receiving areas for receiving a plurality of solid oxide fuel cell stacks; a fuel inlet passageway disposed between a manifold fuel inlet port and a plurality of stack fuel inlet ports; an oxidant inlet passageway disposed between a manifold oxidant inlet port and a plurality of stack oxidant inlet ports; a fuel outlet passageway disposed between a plurality of stack fuel outlet ports and a manifold fuel outlet port; and an oxidant outlet passageway disposed between a plurality of stack oxidant outlet ports and a manifold oxidant outlet port.
Further advantages are achieved and disadvantages of prior art approaches are also overcome by providing a method for using a base manifold for a modular solid oxide fuel cell assembly, comprising receiving a plurality of solid oxide fuel cell stacks relative to the base manifold; distributing fuel to the plurality of solid oxide fuel cell stacks through the manifold; distributing oxidant to the plurality of solid oxide fuel cell stacks through the manifold; collecting fuel stream flow from the plurality of solid oxide fuel cell stacks through the manifold; and collecting oxidant stream flow from the plurality of solid oxide fuel cell stacks through the manifold.
The above-described and other features and advantages will be appreciated and understood by those skilled in the pertinent art based upon the following description, drawings, and appended claims.